Eleanor Catton is an extraordinary writer. Her first novel, The Rehearsal, was a marvellously peculiar and technically perfect story of a story within a story  or stories, actually  that had the reader's mind spinning with the complexities of its narrative invention. The plot  a group of teenage girls acting out the consequences of a sex scandal at their school  was set loose from the very premise of storytelling. Whether what was taking place on the page was an account of events or only words in a script, no more than a rehearsal for what may or may not have happened  none of it mattered. It was wild.

The Luminaries is every bit as exciting. Apparently a classic example of 19th-century narrative, set in the 19th century, with all the right-sounding syntax, clothing and props, the project twists into another shape altogether as we read, and continue to read. The book is massive  weighing in at a mighty 832 pages. But every sentence of this intriguing tale set on the wild west coast of southern New Zealand during the time of its goldrush is expertly written, every cliffhanger chapter-ending making us beg for the next to begin. The Luminaries has been perfectly constructed as the consummate literary page-turner.

But it is also a massive shaggy dog story; a great empty bag; an enormous, wicked, gleeful cheat. For nothing in this enormous book, with its exotic and varied cast of characters whose lives all affect each other and whose fates are intricately entwined, amounts to anything like the moral and emotional weight one would expect of it. That's the point, in the end, I think, of The Luminaries. It's not about story at all. It's about what happens to us when we read novels  what we think we want from them  and from novels of this size, in particular. Is it worthwhile to spend so much time with a story that in the end isn't invested in its characters? Or is thinking about why we should care about them in the first place the really interesting thing? Making us consider so carefully whether we want a story with emotion and heart or an intellectual idea about the novel in the disguise of historical fiction  There lies the real triumph of Catton's remarkable book.

As in her first novel, Catton manages her multiple storylines with deft assurance, winding up a skein of a mystery that's rich with secrets, sex and opium, a doomed love affair, murder and double dealing. It opens like a play, in a town called Hokitika, late at night  with an English gentleman blown through the door of the local inn, out of the weather and straight into the midst of a very strange crowd indeed. "The twelve men congregated in the smoking room of the Crown Hotel gave the impression of a party accidentally met. From the variety of their comportment and dress  frock coats, tailcoats, Norfolk jackets with buttons of horn, yellow moleskin, cambric, and twill  they might have been twelve strangers on a railway car, each bound for a separate quarter of the city that possessed fog and tides enough to divide them."

The sense of staginess here, of set design and costume and figures placed in a room, recalls Henry James's The Art of the Novel, when he writes about managing plot and drama as though directing a play. Full of theatrical detail and action that reads as carefully as stage directions, everything about the way this story is presented makes us think of James's "divine principle of the scenario".

In the same way, this drama relies on the confessions and revelations of its players who, one after the other, relate their version of events  it's both a realistic-seeming account of characters' individual actions and a melodramatic, highly wrought, artificial piece of tale-telling. The way that tale is told changes throughout the book, too, moving from a story told by insiders to an outsider, to the narration of a series of connected events, finally ending with its beginning. All the time, Catton wants us to be aware that this is fiction we are involved with (an authorial presence is generally referred to; there are numerous hypertextual moments that underline that fact, with the word damned appearing as d___ed; introductory summaries are given at the start of every chapter). Her commitment to the artificiality of her project is complete.

But the problem is that as we read on, we don't read in. It is a curious act of double-writing that Catton has achieved  that she could write more and more about a thing, only to have it matter less and less. The characters don't gain depth as the story proceeds; they slip further away from us. The more words given to them, the less we know anything much about them. The last section of the book is an act of bravado analepsis, with chapters thinning out into mere pages as the backstory is laid out.

The same intriguing, undoing kind of writing works on the world of the book, too; its setting and details. So we may read and read about the weather, about the interiors of rooms, the costumes people wear, the food on their plates, the New Zealand riverbank and mists and waters, the sound of its rain hammering on a tin roof  Yet these details don't come together to be compressed into a reality we care about and inhabit. If the book has been made as a kind of stage, then these are the stage sets  not real to look at, only made of paper and glue. In the end, Catton's wondrous 19th-century New Zealand and its rivers of gold may as well be as far away from us as the colony would have been once to a British reader. Out of sight, out of mind.

Those girls in Catton's first novel, literary constructs though they may have been, gathered up our concern as the story went on. We were involved in what happened; we cared about those words on the page. Here, it is as though the opposite is made to be the case. Catton has created her own world in The Luminaries  an upside-down, southern hemisphere kind of a place with its own astrological calendar that casts its own kind of influence, its own light. The clue is in the title, after all, and in the confusing frontispiece that the publishers might have made more of, to alert the general reader to the fabulous trick of the book they hold: that this great, intricately crafted doorstopper of a historical novel, with its portentous introduction, astrological tables, character charts and all the rest, in fact weighs nothing at all. Decide for yourself, Reader, at the end of all your reading, what you think of that: is "nothing" enough?

 Kirsty Gunn's The Big Music is published by Faber.

Eleanor Catton's second novel begins one wet January night in 1866 as Walter Moody, fresh off the boat to make his fortune on the New Zealand goldfields, enters the smoking room at the Crown hotel in Hokitika, "a town not five years built, at the end of the world". Outwardly composed, but "carrying a leaden weight of terror in his gut", he's preoccupied by the memory of a ghoulish apparition he encountered on his passage, doubting his faculties and all at sea inside himself. But before we can hear Moody's tale, an even more mysterious one must begin, for he has stumbled upon a clandestine council of 12 men, "convened in stealth" to discuss a snarl of unsolved crimes.

Two weeks previously, on the night of 14 January, the lives of five individuals shifted their courses: the wealthy prospector Emery Staines vanished; Anna Wetherell, an opium-addicted prostitute, attempted suicide; Crosbie Wells, a down-on-his-luck drunk, was found dead in his cottage, in which was subsequently discovered an enormous fortune, then claimed by a wife, whom nobody had heard of; the brutal ship's captain with a chequered past, Francis Carver, hot-footed it from Hokitika in the middle of the night; and the politician Alistair Lauderback arrived in the town, ill-fatedly encountering both the bodies, the first already dead, the second near lifeless, of Crosbie and Anna, on the road instead of a fanfare of welcome.

So far, so Wilkie Collins down under  a tale of adultery, theft, conspiracy, trafficking, blackmail and murder set against the backdrop of the gold rush, opium dens, seances and tarot cards  but The Luminaries is a dazzling feat of a novel, the golden nugget in this year's Man Booker longlist, a pastiche quite unlike anything I've ever come across, so graceful is its plotting and structure.

The first part of the novel, nigh-on 400 pages, is one of the most beautifully and intricately mapped pieces I've ever read  the recollections of the 12 different men of a single day, 27 January, the day on which the story begins, the "disjunctive and chaotic" events of which lead to their incongruous night-time meeting, all woven into a narrative as smooth and gleaming as a piece of newly spun silk, told in perfect chronology, "in deference to the harmony of the turning spheres of time". And it's to the spheres that she turns for the structure of what could otherwise be an unwieldy tome  each of the novel's 12 parts decreasing steadily in length to mimic the waning moon throughout its lunar cycle.

The 12 men are a motley crew  a Maori gemstone hunter, a banker, a newspaperman, a hotelier, a goldfields magnate, a Chinese goldsmith, a commission merchant, a chemist, a shipping agent, a justice's clerk, an opium-smoking hatter, and a chaplain. They are the fixed stellar constellations of the tale (incredibly, each man's individual astrological chart directs the role he plays in the action that unfolds), interconnected in a "strange tangle of association", around which orbit the planetary characters of the piece, three external pairs  "the widow and the trafficker; the politician and the gaoler; the prospector and the whore"  and Moody, the "unraveller", the detective.

On first setting foot on New Zealand soil, he looks up to the heavens, disorientated by the unfamiliar patterns above. But even here, "in the black of the antipodes, where everything was upended and unformed", a string of apparent coincidences are discovered to be points in a complex labyrinth of entwined fates and fortunes. After all, "what was a coincidence, Moody thought, but a stilled moment in a sequence that had yet to be explained?"